text:
Which aircraft can fly at FL600 or above?
I would like to know some examples of aircraft (specific models) which can fly at FL600 or higher.
I am interested in aircraft which can or could fly at that altitude on a regular basis (service ceiling included). Space exploration or launcher systems are out of the scope.
As far as I know, commercial airplanes cannot fly that high so I can only think of jet fighters, aerostatic balloons, and rocket-powered aircraft.

Are you interested in one-offs and limited-production aircraft such as White Knight Two?

@Mark I am interested in aircraft which often fly (or have flown) in that altitude range. But any other "experimental airborne system" is welcome as well.

Commercial Airliners:
Both Concorde (service ceiling FL600) and the Tupolev Tu-144 (service ceiling FL660) could reach FL600. Most airliners have a service ceiling of around FL410 though.
Business Jets:
According to this article the highest service ceiling for various business jets is at FL510, so none can reach FL600.
Military Reconnaissance Aircraft:
The Lockheed SR-71 Blackbird had a service ceiling of FL850 and routinely operated above FL600. Many other aircraft in this category (e.g. MiG-25, Tsybin RSR, U-2, RB-57F, M-17 and M-55) can also fly above FL600.
Military Fighter Jets:
Most fighter jets have a service ceiling below FL600, but there are a few that can fly higher (e.g. F-15 and F-22 with service ceilings of FL650, the MiG-25 again, and  MiG-31 with the highest service ceiling of FL820+ for a fighter).
Experimental Aircraft:
Wikipedia has a list of altitude records, often by experimental craft. The 60,000 feet limit was surpassed around the end of the second world war with the advent of rocket and turbojet engines. Two notable achievements:
The rocket powered X-15 reached space twice. In 1963 it climbed to 67 miles, nominally corresponding to FL3530. Note that the X-15 did not self-start.
The glider (!) Perlan II has a service ceiling of FL900 and actually reached 76,124 feet. It utilizes standing waves forming at mountain ranges which under certain conditions can extend into the stratosphere. From wikipedia: "A sailplane at 90,000 feet altitude flies in approximately the same aerodynamic regime [...] to be experienced by a moderate size aircraft flying near the surface of Mars."

High altitude balloons and rockets can of course fly higher.

As I recall, the U-2 (in the Reconnaissance class) also operated above FL600, though I don't remember its service ceiling (which was limited by "coffin corner", where Mach limit of the airframe intersects stall speed).

James May goes to 70000 feet in this vid https://www.youtube.com/watch?v=w-COlil4tos but at that altitude there is still 40kts margin above stall and they are still climbing and bleeding speed, so the U2 could make it to at least 75000.

There's also the RB-57F Canberra. I think NASA still has a few flying.

@FredLarson they do.  One of NASAs WB-57's was used to record infrared video of the Crew Dragon In Flight Abort test earlier this week.

Not saying you're wrong, but I expected to see the MiG-25 in the "fighter jet" section.  Interesting to learn it was considered a "Reconnaissance Aircraft".

@JPhi1618 Yes, it kind of belongs to both categories...

I took the liberty of editing in M-17 & M-55. Punched them under the reconnaisance category, M-55 is basically a research aircraft, but I bet that it's not solely used for scientific purposes ;)

... and added MiG-31 as the highest flying fighter jet, service ceiling is reported to be 82000ft

@Jpe61 Thanks! I turned this into a community wiki post now since several users contributed already. This should make it easier for others to make additions...

@ZeissIkon According to Wikipedia ceiling is FL800.

Sorry for messing with the indentation. Apparently the editor in iOS app can’t cope with formatting too well, or I can’t find the right buttons. Could someone fix, please?

While Tsybin RSR was designed to have a high ceiling, it never made it past initial testing - all actual flights were done on a simplified flying lab with reduced performance (it never flew higher than 4000m, for example). The finished aircraft never flew, so I don't think it belongs on this list...

@JPhi1618 the reconnaiscance versions of the MiG-25 could fly higher than the fighter versions, not sure how much higher. They're probably lighter because they lack the wing pylons for the very large missiles carried on the fighter.

@DanilaSmirnov and if it does, so do several very similar US and UK designs from the same period

Since the OP asked for rocket planes -- X15 qualifies. Perhaps other experimental aircraft? Unmanned?

Depending upon the definition of Service Ceiling the English Electric Lightning just squeaks into the military fighter list.  For early variants, if the climb profile was carefully managed, it could operate for about 90 seconds at FL600 before the airspeed bled off to the stall point.

While interesting, I don’t see how this answers the question as asked by the OP.

@dalearn The OP asked I am interested in aircraft which can or could fly at that altitude on a regular basis.  if the Lightning could do it, even if only for a short period, why isn't it a valid answer to the question?

@Graham the poster says that it depends upon the definition of Service Ceiling, but It seems like the EE Lightning had a negative rate of climb at FL600, which would mean it is not an answer.

Maybe not, but English Electric certainly belongs on the list, thanks to the original Canberra (leading to the RB-57)

There's a difference between "flying at FL600" and "reaching FL600 in a zoom climb".


text:
Has color vision deficiency ever contributed to any incidents in aviation history?
I would like to know if there are any official reports pointing Color Vision Deficiency (CVD) as a major contributing cause of an air accident/incident. Not only related to flying but also maintenance or ATC for instace.
So far, I have only come across with FedEx flight 1478, in which a CVD F/O misjudged the PAPI lights. However, the report does not point how severe was the F/O's deficiency (all crew survived the accident). And more important is that the Captain and Flight Engineer (with normal color vision) could neither detect the wrong glidepath.
My final goal is to research the topic of color-blindness in aviation with real case instances and hopefully draw some conclusions about the actual impact of this disease in aviation for candidate's medical certification.

CVD is only disqualifying for night flying or "color signal control". I don't think this is one of the regulations that is "written in blood" as many others are. Many flying cues are by color and if you can't distinguish colors, you need restrictions.

Things in general are so much more flexible now.  In Canada at least you can hold a Cat 1 while blind in one eye and even with Type 1 diabetes (albeit with a lot of restrictions).

@RonBeyer Yes, there is no doubt that aviation jobs require color discrimination capabilities. The thing is that CVD varies greatly among candidates. The issue here is where to draw the line where safety is not compromised. My own experience has shown me that values are kept very conservative using empyrical tests (such as Ishihara test plate) and I am afraid that a more pragmatic approach is missing. For instance, creating simulator scenarios where color discrimination is at stake for safety.

Have you read how they test for CVD? A flight test is part of a class 1/2 medical (which is required for commercial purposes). Maybe we aren't talking about the same country? A "color vision medical flight test" is an actual flight test with a medical examiner... If you pass that, you get your license without restrictions. If you fail you get your license with restrictions...

@RonBeyer I live in Spain, so I tend to think in terms of EASA's regulations. I know that FAA regulations can grant a color vision waiver which implies a "color vision medical flight test". Sadly, we don't have that in Europe. Here, a CVD candidate can get his 1/2 medical certification restricted to fly only under VFR in day time. For someone who wants to have fun with his PPL, this might not seem a problem. But I greatly doubt that any airline would hire a pilot with such restriction.

@ppinto Please add country-specific tags to your question if you want country-specific answers.

One of the flaws in this line of questioning is that until recently most regulators have largely prohibited pilots with CVD from flying, you certainly won't find 2 pilots in an airliner who both have CVD. This is slowly changing so this question is worth revisiting in maybe 15 years time.

Have you thought about this from a maintenance perspective? Maintenance personnel can't be colourblind at the places I've worked. The reasons given to me are because many aircraft parts including electrical components are identified only by different colour bands... Wires identified by colour... Identifying test patterns on screens...

@Craig I am not sure about the point you are trying to make. But let me explain that the post talks about candidates with Color Vision Deficiency and not full Color Blindness. Obviously, people that lack any color channel would face serious problems in the aviation jobs. But that's not necessary the case for CVD. This kind often struggle with colors that are really close in terms of hue and saturation and, as you would know, colors in aviation are well-separated hue/saturation coded. What I'm trying to adress is whrere the limits in CVD should be impossed based on real data.

@ppinto my point is that an incident could be caused by incorrect maintenance because the wrong component was fitted or something like that. Interpretation type issues have caused accidents before, notably the time there was confusion between the words "expired" and "empty" with regards to oxy cannisters put in a cargo hold, which then caught fire. It wouldn't be a stretch to imagine that there could be a colour interpretation example around somewhere. Just can't think of any right now

@Craig thank you for your clarification. This hypothetical color interpretation incident that you are considereing is exactly what I'm looking for. I would really appreciate if you could bring any real case where this has happened. I will do my research trying to find incidents not only related to pilot color vision but also for maintenance and ATC. I will expand the scope of the question. Thanks again.

In response to two NTSB safety recommendations, the FAA stated that it has only identified three accidents involving pilots with valid medical qualifications in which color vision deficiency (CVD) was cited as a contributing cause.

As you mention above, on July 26, 2002, a Federal Express Boeing 727-200F crashed during a visual approach to Tallahassee Regional Airport in nighttime visual meteorological conditions. The three crew members were seriously injured and the airplane was destroyed in the crash, which the NTSB attributed to “the captain’s and first officer’s failure to establish and maintain a proper glide path.” Because the first officer was flying the plane at the time of the crash, the NTSB cited as one of several contributing factors “the first officer’s color vision deficiency" which interfered with his ability to discern the red and white lights of the precision approach path indicator (PAPI).

On Aug. 29, 1992, an incident occurred in which the pilot of a Mooney 20F with “a waiver for partial color blindness to red and green” landed on a closed runway that was marked with orange crosses in the dirt 50 ft beyond each end. The pilot’s “limited ability to detect the orange-colored marking” was cited as a contributing factor.

One incident involved a Navy F4J lost on Aug. 5, 1980, “when a severely color deficient pilot failed to interpret correctly the colored navigation lights of other aircraft in the area, leading to the false impression of a collision.”

Regarding the severity of the FO's color blindness from FedEx flight 1478, records indicate that he passed all color vision tests during his 16 years as a U.S. Navy pilot but failed a test administered during an FAA medical evaluation in 1995. This failed test indicated that he had a mild red-green deficiency. The FAA issued a first-class medical certificate with a statement of demonstrated ability (SODA), based on his years as a Navy pilot and the results of his Navy color vision tests. He was issued this SODA on all subsequent medical examinations.
After the 2002 crash, the first officer passed the Farnsworth Lantern (FALANT) color vision test, which was designed to differentiate between those with mild red-green deficiencies, who pass the test, and others with more significant red-green deficiencies, who fail. He also passed a light-gun-signal test administered by an FAA medical examiner. However, he failed seven other red-green color vision tests and was determined to have a “severe congenital deuteranomaly” — a red-green deficiency that is the most common color vision defect.
Hope this helps.
References: Werfelman, L. (2008, December). Color deficient?[PDF] Aero Safety World, 38-41. Flight Safety Foundation. Retrieved from:http://www.flightsafety.org/asw/dec08/asw_dec08_p38-41.pdf

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Can a F/O declare "My plane" to the Captain?
Let's presume an airline flight piloted by 2 people: the Captain (assuming PIC role) and the F/O.

Is the F/O allowed to take manual control over the Captain actions?
Under what circumstances?
Could this create safety issues, for instance, the Captain trying to recover control from the F/O?
What does CRM suggest about this matter?

Please note that positive control transfer requires a 2-way conversation. It should go "(FO) My Plane, (CAP) Your Plane, (FO) My Plane".

It's my understanding that Captain is a rank, and PIC is a role. Your question conflates the two terms.

I thought the standard phraseology was "I have control", "you have control", "I have control". As long as the goal (make sure both F/O and capt know who's in control of the aircraft's trajectory) is reached, i supposed phraseology is not that important.

Closely related: https://aviation.stackexchange.com/questions/23839/under-what-circumstances-should-the-pilot-not-flying-intervene-without-asking-fo?rq=1

@ManuH  Each operation can specify what phraseology is expected. Where I fly (USA), "I have the aircraft" is common, but if everyone is standardized to "I have control" that would work equally well. "I have it" would be a poor choice, as "it" is ambiguous & has in fact caused problems. Thus the need for an unmistakeable, and standardized direct object for the statement. But "control" or "aircraft" or "airplane" or etc are all good.

Although related, this question is not a direct copy of the one mentioned above.

Also related: https://aviation.stackexchange.com/questions/40777/does-pilot-monitoring-have-authority-to-go-around-in-exceptional-circumstances/40779#40779

@Jamiec I am aware of the difference between Captain and PIC. My intention was to contextualize the situation and introduce the question. Anyway, I have edited it. Hope it is clearer now. Thanks for your feedback!

@Pondlife the question is very related. However, I am trying to increase the scope of it regarding CRM procedures and safety risks due to a hypothetical pilot communication conflict. Thanks BTW.

Pretty much every FO struggles with this.  Technically yes, in the extreme case.  If the actions of the capt are about to get everybody killed or otherwise endanger the aircraft, the FO is supposed to have the authority and an obligation, after a suitable verbal interchange, to intervene by saying "I have control" and take over.  Generally there needs to be a trigger such as a situation where the capt does something that deviates outside normal operating limits, procedures, or protocols.
If the capt declines to hand over control, because, say, the capt has gone off the deep end, well you have a problem.  But in most cases of suspected suicide by plane for example, the suicidee waits for the other crew member to use the rest room and locks the cockpit door - one unintended consequence of reinforced cockpit doors.
The more likely case is a capt that is disoriented or fixated, and in theory an FO who intervenes with proper procedure and with enough "authority" should be able to do it and a capt is expected to relinquish control in such a situation.
But however well trained the crew is, they are two humans and you can't predict what's going to happen.  Different airline cultures apply this kind of thinking more strongly than others. At some airlines the FOs are encouraged to be maybe a little too forceful for most captains' tastes, questioning everything, and others, it's the old fashioned "shut-up-and-pull-gear" culture.  This is still a serious problem outside of "western" operators, in countries that have strong patriarchal cultures, which is partly why you see so many "expat" American, Australian/NZ, Canadian, British, or European captains at far east airlines.
But even in up-to-date places like Canada, FO inassertiveness can be a problem. First Air 6560, pretty much the only major crash of a heavy in North America in almost 20 years (excluding runway excursions and Sully's adventure), is a classic case of an FO failing to intervene to thwart an incompetent captain who develops fixation tunnel vision and breaks the most basic rules of the book.  Every FO needs to read the Transportation Safety Board report.

totally OT, but wow, looking at the pic of the 737-200 in that wiki article points out just how tiny the original engines were on those things and why Boeing's had to jump through so many hoops to put bigger ones on 'em.

But in most cases of suspected suicide by plane for example, the suicidee waits for the other crew member to use the rest room and locks the cockpit door  In most cases??  Has this happened more than once?  Other than the famous Germanwings 9525, I can only find this incident that followed the same story.

There was also Silk Air https://en.wikipedia.org/wiki/SilkAir_Flight_185  so that's three, and I can't recall any cases of what you would call a physical fight over the controls in order to crash with both seated although maybe one or two have occured, so "most" is not too unreasonable I think, and it's the most likely way someone is going to do it going forward anyway.

@John EgyptAir 990 had an FO wait for the captain to leave but didn’t have a lockout.

Yes, the FO is allowed to take over control from the captain on his own initiative, if the circumstances justify it.
One case that I know off where it saved the day was this incident of Lufthansa. On rotation for take-off the aircraft started to roll. Corrections by the captian only aggravated the situation until very quickly the aircraft's wingtip was almost hitting the ground. The FO assumed control (announcing 'I have control') and restored the aircraft's attitude. After troubleshooting they found out that the roll input on the sidestick of the captain was reversed. (The reason behind this is interesting as well, but off-topic in this question)
Basically if the FO deems that the actions of the Captain are an imminent safety risk to rhe aircraft, he/she must assume control of the aircraft.

This is an interesting one which brings up a problem with FBW systems.  What if the capt, in fixation mode, had hit the override?

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Should the weight of the lifting surfaces be deducted from the weight used to calculate the C of G of the aircraft?
If the aerofoils are creating lift they are doing the work to lift the helicopter.  When the helicopter is hovering, the blades are carrying the weight of the entire ship. The forces on the aerofoils are acting in the opposite direction to gravity which is pulling the ship down. These opposing forces create a situation where the ship is now hanging from the aerofoils.
So would this mean that the weight and balance calculation for the pilot should not include the weight of the aerofoils as this weight difference would affect the C of G?
A fixed wing aircraft would suffer the same results?
My question is, should the weight of the section of the aerofoils of an aircraft  that provide lift be deducted from the weight used to calculate the C of G of the aircraft?

Hello Devon, welcome to aviation.stackexchange! That is quite a wll of text you have posted there, making it difficult to read. Perhaps you can cut it into paragraphs by adding a few line breaks for better readibility and/or cut out part of text to get to the point more quickly.
What is your question actually?To me it is unclear what would you like to have answered.

Hi Devon, I'm with @DeltaLima on this. Please make sure that there is an actual question in your post. aviation.SE is a Q&A site, not a forum to share thoughts. Edit your post to fit the Q&A format and I'm sure you'll find plenty of experts here to help you :) In any case... Welcome !

...and make sure to check https://aviation.stackexchange.com/tour to see how things work around here ! :)

Thanks guys, apologies for the long text. I edited the post to include my actual question at the end. I will edit the post a bit later.

I think I understand your question is "is the airfoil taken into account the same way for helicopters and for fix wing aircraft when computing CG?" but I'm not quite sure.

The center of gravity is relevant for all inertial forces. For example, if you turn, the centrifugal force would be calculated with the mass of all aircraft parts, including wings and rotor blades.
If you want to calculate the loads on the aircraft structure, things depend on the location. If, for example, you want to know the load on the wing root or the helicopter rotor shaft, you use the total mass minus wing / rotor mass times the acceleration to calculate the force.
While there are cases where the wing mass needs to be subtracted, center of gravity calculations must include it.

On a fixed wing, for the dynamic purposes of balance, no.  In the end, other than rotational moments (flywheel effects), aerodynamic forces are unaware of the origins and placement of the mass they are working to affect and whether mass is concentrated in the wings or fuselage are the same thing as far as CG is concerned.
The wing still has to produce 2000 pounds of lifting force for a granite winged airplane that weighs 2000 lbs all up, vs a foam winged airplane that weighs 2000 lbs all up, except for the effects of having mass closer to (foam wings) or farther from (granite wings) the rotational axis and its effect on dynamic behaviour (for example, the inertial effects of having fuel in wing tip tanks).  In other words I can install 500 lbs of lead ballast attached to the wing trailing edges, or put 500 lbs of ballast at the same station in the baggage compartment, and I'll have the same aft C of G problem either way because I can think of the wings and fuselage as a single rigid object.
For structural purposes however, the location of the mass matters a lot.  The wing root bending moment is much higher for the styrofoam winged airplane since load is concentrated in the fuselage, and the granite winged airplane with most of its mass concentrated in the wings could get away with much lighter root fittings.  This is the basis of "zero fuel weight" limits on airliners - the effect of mass concentration on wing bending, and taking credit for mass located out on the wings in reducing wing bending vs mass in the fuselage.
On a helicopter, the rotor blade has to support its weight as well as the weight of the hub and the machine hanging below it, so the weight of the machine has to include the weight of the blades in terms of the total weight the blades have to lift.  But the rotor disc has a flexible connection to the rest, so the disc's C of G is effectively disconnected from the body once the disc is holding the machine in the air (the rotor disc is the "helicopter"; the fuselage is the sling load hanging under it - though this is a more accurate concept for teetering rotor machines than articulating rotor machines).
C of G limits on a helicopter are largely a function of articulation limits between the rotor and fuselage, that is, how far off perpendicular the fuselage's vertical axis can be relative to the rotor mast's axis when in flight.  So helicopter weight and balance calculations allow for the fact that the rotor's mass is part of the G of G of the machine when it is weighed statically, but is factored out of the calculation to establish C of G limits that apply while in flight.
So in the case of the helicopter, the weight of the blades has to be included in all up weight the engine has to lift, but does not affect center of gravity in flight.

Thank you John K - I tried an experiment yesterday when conducting a reweigh on a helicopter. With the helicopter hoisted and left to hang freely, I took a measurement from the tail to the ground. I then got guys to lift the main rotor blades off the stops (this head allows the blades to flap freely on hinge bolts) which removes some of the weight of the blades. The tail measure two centimeters lower during while the blades are lifted which means C of G had changed. Maybe where this experiment is wrong, is that the blades are not yet taking any load and are not actually lifting the helicopte.

@AME  I think hanging it from the rotor mast means the blades are acting on the CG somewhat the same as when sitting on the ground, so that when the blades are lifted the CG moves toward the fuselage-only CG, which with no pilot aboard would be slightly aft of the mast axis, so I would expect the tail to drop.  So I think you got the correct result.

This is a very interesting play on modeling based on the center of lift.   Does a plane just "hang" from its wing?  Is the wing the actual "pivot" for pitch? In reality, all unbalanced forces cause acceleration (acting at the center of gravity) until drag force re-balances to a steady state.  So, like John says, your CG is simply behind your lift point.  Where does the POH say it should be?

The CG when loaded will have a range with limits forward and aft of the mast's axis, which determines how much the machine hangs at an angle while hovering, and also affects the pitch attitude in cruise.  The pilot and front pax have the largest effect.  On very early B-47s you have to move ballast weights between the front of the skid and the tail depending on single light pilot (weight forward) and 3 seated (weight aft) to keep the CG close enough to the rotor mast. The huge horizontal tail of the Blackhawk helped extend the CG range.

You may choose to model the wings (or helicopter rotors) and the rest of the airplane as separate entities linked by springs/dampers to simulate structural connections. Or if the structures are rigid enough for the purpose of your simulation, you may consider the whole thing as one single rigid-body.
But no matter how you model it, the mass of the wing (or helicopter rotors) is there!

JZYL, thank you. Surely though, the aerofoils are not linked to the surrounding “air” mechanically. The interaction between the aerofoil and the air create the lift and that air is not connected to anything else. So I agree the weight is still there but it is being supported by something not connected to the aircraft. The weight goes into the air that that is helping create the lift?

@AME That's a negative. You don't need weight (i.e. gravity) to generate lift. And in any case, in a free body diagram, the lift is just another external force.

Another way to think of it is the blades are generating less lift because of their mass; some of the lift goes to supporting the blades' mass. The amount of lift generated by each blade is different (depending on cyclic position), but the subtraction of lift is the same, therefore the percentage of lift removed is different, therefore affecting the CG.

For a helicopter, yes indeed the fuselage hangs from the rotary hub, although there is interaction between rotor disk and fuselage (the rotor angle is directed by the flight controls, fuselage angle follows).
The weight of the lifting surfaces can be subtracted from the total weight, but that complicates the computation unnecessarily: the weight and position of the lifting surfaces is a known constant. So the moment equations all add and subtract this known constant, and presto: the CoG of the whole helicopter.

For a fixed wing aircraft, suppose #1 has wings made of styrofoam, and #2 has wings made of granite. Exact same shape, very different weight.  Can we omit all that weight in the case of #2 simply because it's part of the lifting surface? Or does it still affect CG calculations?

Well, it's tax time, so why not ask about deductions?
No, you do not change CG, unless weight changes from burning fuel, or weight is removed from the aircraft by dropping items from it.
Thrust forces from rotors and props, aerodynamic forces from motion (lift and drag), and G forces from turning act on the center of gravity.  The net center and magnitude of pitching, rolling, yawing, and lifting forces around the center of gravity determines what the aircraft does.  Once in motion, drag forces must be considered.
Gravity force vector is constant.


text:
Why don't solar powered aircraft use wings with more surface area
I was looking at some solar aviation projects, and I noticed they appear to follow the designs of a glider.

The Helios drone above is basically a flying wing with a high aspect ratio.

And the solar impulse above is a textbook glider with minimal cord length and a long wing span.
I understand the idea is a wing with a high aspect ratio reduces parasitic drag by decreasing its surface area, however in this case don't you want the most wing surface area possible?
This answer shows that induced drag is unaffected by the wings aspect ratio, so if it's only parasitic drag we're trying to combat here, why not keep the wing span the same, but make it's cord longer?
Won't the added solar panels you could fit on a wing make up for any friction drag caused by the longer cord?
Taking this to the extreme could you make some kind of solar powered rectangle that has a width (span) comparable to the gliders above, but a length (cord) twice as long as the span?
Surely you'll have enough power to make the aircraft fly, so are there other design considerations that factor in when choosing the cord length of these solar powered projects?

The question seems to be downplaying the importance of parasitic drag.  The root of the question seems to be  "why doesn't the desire for maximum surface area for solar collection drive the design of solar-powered aircraft toward a lower aspect ratio than we see in practice."

@quietflyer yes I think you could summarize my question as such, but how much of a role does parasitic drag really play? Considering solar panels can provide ~1kw per square meter isn't that enough power to compensate for the added drag?

It's an interesting question-- consider the Solar Impulse-- they could collect enough power to fully charge the batteries after a night of slowly-descending gliding-- it's not clear how more chord would have helped them-- the wing loading was already very low and more chord might have had unacceptable consequences in turbulence and more batteries might have been needed to benefit from the extra cells-- anyway it is a good question and I'm not sure I have a specific suggestion for improvement here.

@quietflyer actually your mention of batteries might explain it. It's not so really how much power these planes can produce in full sun, but the performance of the aircraft when flying at night on batteries. Batteries are heavy, and I think these projects are more about all round performance, than just daytime.

It is not clear to me what is your main question here. Do you want to know why your "flying rectangle" is a bad idea? Or just what are the drivers for the aspect ratio chosen for these projects? It does seem like you understand the role of aspect ratio in the drag equation, so if your question is the first one, could you edit the rest out?

@AEhere I'm asking why we've never seen a "flying rectangle" in solar projects. I included the 2 projects I did as references to show how solar aviation is typically designed, but can remove them if you think it's too much. In the comments above it was discussed how nighttime flying may play a role in why rectangles have never been designed, but if you have any more input I'd like to hear it.

My input is that the flying rectangle still needs to fly like an airplane, as solar panels don´t generate enough power to power a TWR>1 craft. Therefore the approach is the same as with gliders, where the span is limited by structural requirements and the chord is limited by the need for a decent aspect ratio. I´ll try spinning this into an actual answer if nobody (read: the glider enthusiasts around here) beats me to it.

@AEhere I'd love to read a real answer about this. Solar panels produce ~1kw of power per square meter, that seems like more than enough to counter parasitic drag, and the few pounds of weight the panels would add. I understand you'd need a longish span to keep the induced drag reasonable, but I don't see anything stopping it. However I'll admit I'm not an expert at running numbers either.

"Solar panels produce ~1kw of power per square meter" didn´t notice that before... are you sure? Sounds way too optimistic. A quick search point to 1kW as the input solar power per square meter on the ground, after the 20% or so efficiency you´re likely to get, that's 200W per square meter. Napkin math: an $11m^2$ ASH 26 motor glider would gain about 2.2kW... well short of the 37kW its real engine produces.

@AEhere Quick google search and you are definitely correct. I was thinking how much sun energy hits per square meter, but solar panels are obviously not near 100%. Sorry for that. However I think the idea still has merit, as the sun seeker duo claims steady flight with 7hp (5kwh), but yeah it makes the margins a lot tighter, and the craft will fly much slower.

@YAHsaves Solar Impulse 2 comes in at 245 Watt/square meter.  But it can generate 50 kW with its four motors to lift over 5000 lbs.  The wing area is 269 meters squared.  So look at that RB-57 as a design possibility.  Remember AR factor is only added to CDo, and lengthening chord may provide benefits in this case.  But it must glide well enough to survive the night.

@RobertDiGiovanni how is the Canberra relevant? I know it looks like it has a large chord, but it is a totally different class, and with a wing loading of $175kg/m^2$ it is hardly comparable to electric craft like the Solar Impulse, with a wing loading under $10kg/m^2$. I am more inclined to think the Canberra had a large root chord to deal with the combination of early jet engines and thin airfoil.

It is the NASA R "arrrrr" B - 57.  That and some writings show that increasing chord may be viable.  The RB-57 can fly very high.  It's the wing.  So we change jets to props and lighten it up...the design still goes high.  They actually did this with the B-36 "featherweight" (reduce weight).  Shame only 4 have survived.  This concept may have legs.

First, because solar panels are pretty mediocre sources of power per area. An industry average found via quick Google search is in the 200 - 300 Watt per square meter range, so let us be very optimistic and take the higher value, $300W/m^2$, for a round of math. If you want the details, solar irradiation on the surface is about $1kW/m^2$ and the best experimental photo-voltaic cell efficiencies by year are graphed here.
Using the ASH 26 motor glider as a case study, we can see if solar powering an aircraft is as trivial as the OP suggests.
Assuming our panels are made of fairy dust we can further decide their weight is negligible and that we can perfectly cover the $11.68\,m^2$ of wing area this glider has and that it will operate as though under normal incidence (Sun at 90° to the panel) all the time. Thus, $3.5\,kW$ of free energy... which sadly is only $9.4\,\%$ of the power supplied by the Wankel engine used on the real glider, and with which it attains a very humble $4\,m/s$ climb rate. This is before even considering that batteries are also very inefficient sources of energy per unit of mass when compared to hydrocarbons.

Now, for the second part of the OP´s query, how about enlarging the chord of the wing to increase the area?
This also happens to fall flat for different reasons. The drag coefficient:
$$
C_D =C_{D0} + \frac{(C_L)^2}{\pi e AR}
$$
has the aspect ratio ($AR = {b^2 \over S}$) of the wing in the denominator of the second term, the so called induced drag (because it is induced by the lift, note the coefficient of lift itself appears in the numerator).
This equation quickly illustrates why gliders have long wings: a higher AR provides a lower induced drag term. The other term, the parasitic drag, is either indifferent to the chord or slowly grows with it due to boundary layer transition in laminar airfoil designs.
We can arrive at the conclusion that for a given surface, a higher-AR wing will be the less draggy solution.
Therefore, the current attempts at solar powered aircraft all attempt to add area by extending the wings, and are limited by structural constraints like bending moment at the root, which you can clearly see them try and alleviate by spacing out the engines into the wings, providing some relief at the expense of increased roll inertia.

“200 - 300W range”: 300 Watt per elefant? Or per potato? Or?

@JanHudec I deserved that sass. Fixed.

Thank you for drawing this out on paper, it helps to see the numbers. One thing I didn't understand though, is I mentioned in my question how the induced drag doesn't actually increase with cord length. Are you suggesting the answer I linked to is incorrect?

@Peter Kämpf tends to be right so listen to him. Maybe II can make the answer clearer... or maybe I´m wrong and need to go back to school. Do note that Peter's calculation is for two wings of the same span, so he can allow one to have twice the surface of the other. Since span and area are the usual variables that are set by outside requirements, that approach makes a lot of sense. If you want to compare two wins of the same surface area, things change.

Note that intensity of Sun light is around $1\ \mathrm{kW}\cdot\mathrm{m}^{-2}$, so $300\ \mathrm{W}\cdot\mathrm{m}^{-2}$ is 30% (at perpendicular insolation; don't forget to multiply with appropriate cosine as wings have to be approximately level to support the aircraft and the panels can't therefore be turned towards the Sun), which is actually pretty good efficiency. IIRC green plants manage only about 4%.

@JanHudec that's why I stated normal incidence and said I was being very optimistic. Could be clearer but...

@AEhere, sure. I mainly wanted to point out that the panels are mediocre sources because Sun does not provide that much in the first place, not because they would have poor efficiency.

@JanHudec I added that graph, but mostly because I do love throwing it at solar power fans :)

$C_{D0}$ is proportional to wetted area? Or is it a form factor, multiplied by the wing area?

@Koyovis you are right, it is a factor, it is the resultant parasitic contribution that scales with area.

Adding chord to an existing wing does the following:

It increases wing area S
It reduces aspect ratio A
It increases weight.

These three factors influence each other and should all be considered.
Drag D of a sub-sonic fixed wing aeroplane is
$$D = C_D \cdot \frac{1}{2}  \rho  V^2 \cdot S = \left( C_{D0} + \frac{{C_L}^2}{\pi  A e }\right)\cdot \frac{1}{2}  \rho  V^2 \cdot S \tag{1}$$
Lift L = weight W (a valid approximation at stationary flight at small angles):
$$L = W = C_L \cdot \frac{1}{2}  \rho  V^2 \cdot S => C_L = \frac{2 \cdot W}{\rho   V^2 \cdot S} \tag{2}$$
Substitute (2) into (1):
$$D =  C_{D0} \cdot \frac{1}{2}  \rho  V^2 \cdot S + \frac{2  W^2}{\pi  A e \cdot  \rho  V^2 \cdot S} \cdot \tag{3}$$
With:

S = wing area
A = aspect ratio = $b^2 / S$ with $b$ = wing span
e = Oswald factor, accounting for varieties in profile drag, lift distribution, interference.

Substitute $A \cdot S = b^2$ in (3):
$$D =  C_{D0} \cdot \frac{1}{2}  \rho  V^2 \cdot S + \frac{2  W^2}{\pi e \cdot  \rho  V^2 \cdot b^2} $$
So now we can see what increasing chord does while keeping span the same

It increases S with increasing chord
It increases weight with increasing chord
It decreases e with increasing chord
It decreases $C_{D0}$ with increasing chord if only chord is added to the wing profile and thickness stays the same - relative thickness decreases and $c_d$ decreases. $C_{D0}$ remains the same if both chord and thickness are increased proportionally.

Three out of four factors above increase drag with weight being a quadratic factor, and we're hoping to offset the increase in drag with more propulsive power. We're increasing drag, weight, complexity, cost...
Prudent aircraft design would be contrary to this.

The simple answer is: If you add area, do it at the tips as well.

"It decreases $C_{D0}$ with increasing chord" I can't see that from the equation presented, it seems to me $C_{D0}$ is a coefficient multiplied by $S$. For an equal span an increase in chord will increase $S$ and thus the contribution of the parasite term.

@AEhere have added into the answer.

@Koyovis fair enough, I didn't think you were operating on the airfoil itself. The pedant in me does want to point out that this might not be a general solution: at low $Re$ adding to the chord may trip the boundary layer and raise drag, but I don't have any numbers handy to argue how much of an impact this has compared to the relative thickness reduction.

@Koyovis Wouldn't "S" and "weight" be increased no matter what? If the aircraft needs x amount of power to fly, and you need more solar cells to reach x, increasing the the span will still effect both these properties. I'm not familiar with how to solve for "e", but I guess the cord changes it enough to be significant?

@YAHsaves Weight is minimised very scrutinously. S is a major design parameter: W/S is the wing loading, which is determined in the pre-design, it is optimised for lowest drag. Lower weight, lower surface area and higher wing loading all decrease drag.

@Koyovis So basically the wing has a limited surface area to play with. Since increasing the span while keeping the cord the same would also increase "S" and weight. I guess what you're saying is we really need more efficient solar cells, instead of just trying to make the surface area larger somehow. Is that correct?

@YAHsaves Yes the wing surface area is optimised for minimal drag. The whole design is a multi-dimensional matrix with very many in- and outputs, with aerodynamic optimisation having adverse effects on constructional weight and vice versa. Unfortunately, a "just add water" approach doesn't work in aeronautical engineering.

You definitely could add chord to the wings, but it is the same question of efficiency.  Rarely do you sacrifice aerodynamic efficiency to carry more weight.
But in this case the benefits of adding chord to increase surface area have merit, although keeping aspect ratio the same and simply making the whole wing bigger may be a choice as well.  And let's not forget the possibility of adding area to the tail too.
Another possibility is to scale up the size of the aircraft, as weight per surface area increases with size.  Improving the efficiency of the solar cells and the charge carrying capacity of the batteries also helps.
Also, take note of the span loading benefits of the NASA aircraft.  (a little more weight on the ends may have been an improvement)

Yes I agree you could scale everything up while keeping the dimensions proportional. However that has it's own problems, 1) longer spans are harder to store/find landing for ect.... 2) weight is a product of volume which is multiplied by 3 directions, while surface area is a product of 2 directions. Which means weight scales faster than surface area. So keeping the geometry the same, but scaling things up will get heavy. I guess I'm asking could you offset these potential negatives using the geometry proposed in my answer?

A wider wing is certainly stronger. And you can even consider 2 wings! Yes, lifting capacity would have to match weight, so greater chord and thicker scale up is possible.  Desired cruising speed is another very important consideration.

@YAHsaves a design you may look into is the RB-57 Canberra.


text:
Is the pod on the right wing of the PC-12 and Cessna 208 a gyrocompass?

Hello avgeeks,
First time posting here looking for an answer.
Could someone tell me what's located inside that pod on the right wing of some planes like this Pilatus PC12 or this Caravan 208?
I guess it can be a gyrocompass but i am not 100% sure.
Thank you in advance!!
Safe landings.

Related, maybe a dupe?

"Hello avgeeks,"?

Its not the gyrocompass. Its where the weather radar unit is mounted since the prop prevents it from being mounted in the nose like on many larger aircraft. You can find a nice instructional video on how to use it here. The magnetometer used on many aircraft to provide magnetic heading information to the systems is much smaller than those domes.

(source)
If you are referencing the heading indicator when talking about a gyrocompass those are panel mounted. If you are referencing the wet compass (which is balanced in fluid) those are mounted on the column in the center of the windshield typically. A lost of the more modern aircraft in this class have glass panels which use AHARS units and may not have traditional gimbals anymore.

The gyrocompass can fit inside the old "round gage" housing on the control panel.  With a glass panel, it's most likely mounted behind the panel somehwere.

The "flux valve", the magnetic sensing part of the gyrocompass, is usually out near the wing tip but they are able to fit into the wing structure so you can't see them.

A whiskey compass (not wet compass) is called that because it is filled with alcohol, or some kind of oil.  Glass panel heading indicators, which are replacing the heading indicators, use a magnetometer located in the rear fuselage or out in a wing, to provide the magnetic heading info that is displayed.

@CrossRoads I have corrected the water mistake.

A lot of planes have also gotten away from the "wet compass" and instead use a Vertical Card Compass, which presents a layout and heading reading that matches the reading on the heading indicator (be it gyro based, or a glass panel). The Vertical Card Compass may still be installed above the glareshield/on the window, or may be mounted in the panel, more as a backup when a magnetometer is used.

Wow thank you guys! especially @dave , really good answer, it was exactly what I wanted to know. Thanks:)


text:
How much fuel does an airliner consume during passenger boarding?
As I understand, sometimes APU is running during the passenger boarding. How much fuel do the APU consume during this process?
Of course, it must depend on the total boarding time, so I think it should be estimated in amount of fuel consumed per minute.
Is there an approximation for different aircraft sizes? How does it change if the aircraft is connected to GPU or PCA?

APU's and GPU's are not necessarily the same thing. Many GPU's are gas or diesel reciprocating engines with much lower fuel burn than a jet APU. Typical Recip GPU are 10-20 gph while APU's are 50-200 gph.

Another complication is that a typical GPU does not provide compressed air and so cannot be used for starting the propulsion engines: the APU needs to be started at some stage, (or yet another huffer/ASU cart lugged over).

This depends on the aircraft and airport and how they are equipped. The time varies as it takes between 30 and 120 minutes to turn around an aircraft. So ill provide GPH numbers that can be used as desired.
Some airports have umbilicals that can provide ground power. This is often fed via a cable that feeds out of the terminal. This is usually fed from what ever power supply is feeding the airport.
Some airplanes (many these days) have an APU (auxiliary power unit). These are capable of feeding the power demands during a turn around. The also make it far safer for the ground crew by not having the engines running when there is crew on the ground working around them. The fuel burn of an APU can be found in the answer to this question.
Some airports supply power through the use of a ground power unit. These can be diesel powered or run on Jet-A and their output varies. They even have them for the small GA aircraft I fly to charge the battery if it dies on the ramp. This article lists a burn of 5 gallons an hour for a GPU although sizes vary. This maker lists their GPU's by Gallon per kilowatt hour which may be more appropriate for matching load demands.

Some ATR also have the possibility to use an "hotel" mode (and also maybe some helicopters)  https://aviation.stackexchange.com/questions/1790/what-is-hotel-mode-on-a-turboprop-engine Not sure if it is worth mentioning since it seems to be rather an edge case


text:
Are mode C altitude returns valid for aircraft separation?
According to FAA JO 7110.65 5-12-8 'Validation of MODE C READOUT', Mode C is valid if there is less than 300 feet deviation from the pilot reported altitude.
If ATC instruct 'A' aircraft to maintain 5,000ft, and its Mode C indicate 4,900ft on radar, and ATC instruct 'B' aircraft to maintain 6,000ft and its Mode C indicate 6,000ft, are A and B vertically separated?
By looking radar, it is 900 feet separation, but pilot reported altitude is 1,000 feet separated.

Yes, they are separated. Both according to mode C (in your example, there is 1,100 ft between them - not 900) and in general. It is normal for there to be small deviations in mode C in the range of 100 to 200 ft. If I have two aircraft crossing each other, supposedly with 1,000 ft in between, but the indicated (mode C) separation is slightly less, I will certainly ask the pilots if they are indeed at their assigned altitudes. If they confirm, then all is well. A pilot report generally overrules mode C (to the extend where there is even a procedure for asking the pilot to turn off mode C reporting if there is a discrepancy between pilot report and mode C).

The IFR-IFR separation standard is 1000ft precisely to accommodate altimeter error.
For instance, if the lower aircraft is actually 300ft higher than assigned (5300ft) and the higher aircraft is actually 300ft lower than assigned (5700ft), then they are 400ft apart, which is still safe though obviously not ideal.
The standard for IFR-VFR or VFR-VFR separation can be reduced to only 500ft (less than the combined margin of error) because the aircraft should be able to see and avoid each other in the event of worst-case altimeter errors.


text:
Does two-way communication failure include one-way communication failure?
Code 7600 means lost communication, more specifically two-way communication failure. I wonder whether two-way communication failure means losing the capability of maintaining two-way communication or  not? If the pilot can only hear but not transmit, is it also included in two-way communication failure?

7600 means a loss of two way communications, it's a way of letting ATC know you have a problem sending or receiving, or both.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Are there limitations on taking off or landing if airport lighting such as the VGSI (PAPI) is out of service?
There are many types of airport lighting that aid pilot to land safely such as ALS, VGSI or runway lights. And some instrument approach procedures state that their weather minimums must be raised in case the ALS is out of service.
However, I think those aeronautical lights are not essential for pilots, they're just aids. In case the airport lighting such as VGSI (PAPI) is out of service, are there limitations for landing or take-off?

I've taken off and landed at airports without working PAPI/VASI and all they stated in the NOTAM was that it is out of order. For ILS you would still have a glideslope, VFR pilots can usually get it in without them. This isn't an answer because I don't know if it changes anything in the commercial world, but it doesn't change anything in the GA side.

Are you asking about the rules in a specific country? Airlines also have their own operating procedures that might apply here.

Surely not, at least in the US in the VFR context.  IFR may be a different story.

There wouldn't be any limitation on taking off with the VASI/PAPI out of service, unless it involved a requirement to return to the airport where the VGSI would be required (see below).  That would be a very extreme case, because it would mean that

the rules + the existing weather require the ability to return to the departure airport (i.e. a "takeoff alternate" is either not authorized or none is available), and
no other runway (including the same strip of concrete, landing in the opposite direction) is available at the same airport (tailwind component could cause this), and
this is a case (discussed below) where a VGSI inop prevents an approach to 'this' runway.

That's going to be a very rare combination.
So, when can an inop VGSI prevent an approach?  There are cases where US TERPS rules do require an operative VGSI in order to conduct certain operations -- mostly at night.  I've seen plates where a VGSI is required for circling operations to a given runway at night, and in one case where you couldn't fly any instrument approach, even an ILS, to the particular runway without the VGSI.
The latter fell in the category of TERPS rules that don't make intuitive sense... if I'm flying the ILS glideslope, by the time I'm going visual I'm so close to the runway that you'd think obstacle clearances have all been met & nothing remaining (in front of the aircraft) could possibly be a factor.  It was a memorable discussion because it seemed to make so little sense.  But, the restriction was published, and without the VGSI that runway wasn't usable.
The general case, however, is that the VGSI can be inop with no effect on the ability to fly an approach.  In 99.9% of the cases, it won't matter.  But for an obstacle in the right spot, you can get the note on the approach plate stating the requirement, and in that case, it matters.
But it's very uncommon.


text:
What is the difference between the ILS Critical Area and the ILS Sensitive Area?
What's the difference between the ILS Critical Area vs ILS Sensitive Area?
I'm getting multiple conflicting opinions online.
e.g. I can't decipher from this set of definitions how exactly they differ:

The ILS critical area is an area of defined dimensions about the
  localizer and glide path antennas where vehicles, including aircraft,
  are excluded during all ILS operations. The critical area is protected
  because the presence of vehicles and/or aircraft inside its boundaries
  will cause unacceptable disturbance to the ILS signal-in-space

vs

The ILS sensitive area is an area extending beyond the critical area
  where the parking and/or movement of vehicles, including aircraft, is
  controlled to prevent the possibility of unacceptable interference to
  the ILS signal during ILS operations. The sensitive area is protected
  against interference caused by large moving objects outside the
  critical area but still normally within the airfield boundary.

All I can grok is that the critical area seems some subset of the sensitive area?
Do I take this to mean no vehicles are allowed in critical area but some smaller vehicles may be allowed in the sensitive area?

Where are you getting these terms and definitions from? I've not heard of ILS Sensitive area in that context.

@slookabill I could be wrong. I'll try to post my source but so far as I remember it was NOT authoritative. If you have a different definition / concept in mind I would love to hear.

Basically, yes- critical area is a subset of the sensitive area. However, the terms 'sensitive' and critical' are used interchangeably in many contexts. ICAO itself acknowledges this in the same section (ICAO Annex 10 Volume I Attachment C):

Note 1.— The objective of defining critical and sensitive areas is to afford adequate protection to the ILS. The manner in which the terminology is applied may vary between States. In some States, the term “critical area” is also used to describe the area that is referred to herein as the sensitive area.

The determination of the critical and sensitive areas depends on the actual airport and the system in operation. The operator/regulator may simply include the are in critical list if they suspect any interference. For example, Transport Canada says:

Actual critical areas can be defined only by experimentation and experience. When any portion of a designated sensitive area becomes suspect as a likely source of interference, that portion must be included as part of the critical area.

The main difference appears between the critical and sensitive areas appear to be that the size of the critical area is fixed (for a localizer and glide path antenna in an airport) while that of the sensitive area varies with the category of ILS and the aircraft type. In fact, the introduction of A380 led to a reassesment of ILS protection areas. From Volume I:

2.1.9.3 The size of the sensitive area depends on a number of factors including the type of ILS antenna, the topography, and the size and orientation of man-made objects, including large aircraft and vehicles. ... . Because of the greater potential of the larger types of aircraft for disturbing ILS signals, the sensitive areas for these aircraft
  extend a considerable distance beyond the critical areas.

Image from ICAO Annex 10 Volume I Attachment C
In operational sense, in critical areas, all the vehicle and aircraft movement is prohibited, while in sensitive areas, the prohibition is limited.

To protect the critical area, it is necessary to normally prohibit all entry of vehicles and the taxiing or parking of aircraft within this area during all ILS operations. ... With respect to sensitive areas, it may be necessary to exclude some or all moving traffic depending on interference potential and category of operation.

As you can see from this ICAO Annex 10 image, the ILS critical Area does indeed lay within the ILS sensitive Area, and its size is dependent on the Category of the ILS approach.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Are there different sub-types of a mayday call and do pilots use them when declaring emergencies?
I was reading this pilot's quote from the Northwest Airlines Flight 85 incident:

"This was a classic application of CRM. We were blessed and lucky that
  we had full flight crew augmentation. We had four pilots to work
  together in the cockpit. We had an excellent group of flight
  attendants on board; that became important later because we briefed
  this as a ‘red’ emergency, which means there’s at least a solid chance
  you’re going to have to evacuate. We weren’t sure we were going to be
  able to keep the airplane on the runway."

I'm aware of the Mayday call but does it have sub-categories?  He refers to a "red emergency". Do pilots always classify their emergency into sub-types when they declare it?
Any explanations on what the various sub-types are and how they are classified?

Guessing this is airline specific

The quote is not about the Mayday call, but the briefing between flight and cabin crew regarding risk of needing to evacuate. These are mostly unrelated.

The simple answer is no, there are no "subclassifications" of emergency or urgency calls in standard aviation phraseology. In terms of priority, they are all the same; however, in terms of actions taken, there can be differences based on what caused the aircraft in question to make the emergency or urgency call.
There's mayday (emergency), pan-pan (urgency), and everything else (routine traffic). Mayday trumps pan-pan, and pan-pan trumps everything else.
Broadly speaking:

mayday is used when the safety of the flight has been compromised and the pilot(s) require immediate assistance to recover.
pan-pan is used when the pilot(s) require assistance beyond that normally offered by air traffic control, or require priority handling, but the safety of the flight itself has not been compromised.

Compare When should the term “pan-pan” be used instead of “Mayday”? which discusses the difference between the two in more depth.
Yes, there is a bit of overlap between the two: it's possible to come up with situations where it is not entirely clear whether "mayday" or "pan-pan" is more appropriate. When in doubt, it becomes a judgement call. A pan-pan can escalate into a mayday as the situation develops, and even a mayday can be terminated if the situation that called for the original mayday call no longer exists. (The latter could, for example, happen if a GA VFR pilot becomes uncertain of their position, and are then able to identify their position in such a way that the flight can proceed safely; or if a non-instrument-rated pilot flies into IMC, and are able to return to VMC and proceed safely.)
The broad classification of emergency or urgency is then further specified by describing the type of emergency or urgency situation, using either standard phraseology or plain language, as appropriate. The purpose of this, however, isn't to prioritize such calls, but to identify to ATC (and other aircraft) what types of assistance is required.
Compare How does ATC handle different kinds of emergencies?, though that question is somewhat US-specific and specific details can vary between countries.
To mention a few examples, without in any way intending for this to be an exhaustive list:

mayday, VFR into IMC, negative instrument qualified — this one likely requires immediate help in returning to VMC, whatever that entails
mayday, decompression, emergency descent to ten-thousand — no immediate assistance required for that flight, but get everyone else out of their way now, then figure out how and where to get them onto the ground
pan-pan, fuel — this one needs landing priority, and may require vectors to the nearest suitable airport, but not much more than that
pan-pan, passenger ill — this most likely requires notifying someone on the ground so that the situation can be handled when they land, and might require this one flight to divert, but other than that, not a big problem from an ATC standpoint

MAYDAY FUEL is another recognized distress category. https://www.skybrary.aero/index.php/Fuel_-_Regulations

There are advisory reports, such as "Minimum Fuel" which indicate that a possibility of an emergency could happen.  While the FAA is clear in the AIM and the Pilot Glossary, as well as other publications such as InFO 08004, that Minimum Fuel is advisory in nature, many controllers will treat it as an emergency.
I think that this is done sometimes to justify priority handling in dense terminal areas.
One outfit I worked with used condition codes for a variety of situations, including dispatch issues.  However, there is no regulatory basis for that.
Furthermore, there other ways that emergencies are declared, without voice mayday or pan calls.  For example, an IFR aircraft squawking lost communications.  Or an aircraft signaling that they are being hijacked.
Finally, a regional jet reporting, "we need a little delay while we sort out a gear problem" will often get priority handling similar to an emergency.  It could even get (at least in a case I remember) equipment rolling.
In summary, there are non-urgency and non-emergency advisories which while they might be intended to convey information, may or may not result in emergency or at least priority handling. Secondly, there are numerous ways that emergency, urgent or even advisory communications can be conveyed, all of which could be handled as an emergency at the discretion of the controller.


text:
Is it possible for a plane to be over fueled (and over-weight) to take off?
I've just reached my destination after 33 hours going from one European hub to another. A journey which usually takes a max of 6 from leaving my house!
On the final leg of the journey, after boarding, the pilot asked for volunteers to leave the plane as they were too heavy to take off.
They had flown a 50 min flight from my final destination to where I was and, without fuelling, were turning around to go back. They were adamant that the plane was too heavy and (with a print out from one of the flight computers in hand) were asking for 27 people to leave the flight.
Is this possible? Because the MTOW of the aircraft is greater than the max landing weight, how could they have landed under max landing weight but now be too heavy to take off?
Maybe they flew with no passengers, but exceeded MTOW after adding more passengers and luggage?
Any suggestions for question re-phrasing or additional clarity are greatly appreciated.

Can you give us the flight number and day? Or do you remember the type of aircraft? Also, are you sure they did not refuel?

How many passengers were there in total? 27 people isn't that many. But to your question, maybe this flight is limited by runway length or altitude so take off weight is lower than typical.

Sure. To answer both questions in one post:
LH2327, today (11.2.20) A320 Neo.
I'd guess at somewhere around 120 people (two full bus loads). they definitely didn't refuel. They said they filled the plane in Munich the day before to give the plane more balast to cope with the storm winds.
Departing Vienna I wouldn't have thought runway length would come into it.

" They said they filled the plane in Munich the day before to give the plane more balast to cope with the storm winds" -- this is worthy of another question.  Is this possible?  What would be the benefit of more weight, in the context of strong wind?  To increase the span loading and thus decrease the wing-bending stresses at the wing roots during gusts?  To keep the plane from blowing over on the ground? Feel free to adapt any part of this comment into another question.

It's a good question @quietflyer. I'm presuming increased stability but not sure.

The aircraft you flew on was D-AIUX, a Lufthansa Airbus A320-214. On 10 February it was scheduled to fly from Munich to London, but the flight was cancelled due to the storm:

(flightradar24.com)
If the aircraft was fueled for this flight the day before, it would need:

3.13 kg/km x 944 km = 2.95 t of fuel for the trip
about 1.5 t of reserve fuel

After actually flying the 356 km to Vienna, it would have burned about 1.11 t of fuel, resulting in a total weight of:

42.6 t OEW (Operating Empty Weight)
3.34 t of fuel remaining
+any payload

The MTOW (Maximum TakeOff Weight) is 78 t, which would therefore still leave 32.06 t for payload, but the maximum payload is 19.9 t for the A320. So this cannot be the limiting factor.
It was noted that the runway could limit the takeoff. Your flight departed from runway 29, which is 3500 m long:

(flightradar24.com)
The A320 only needs 2100 m at MTOW for takeoff, so this was also not the limiting factor.
You said "they filled the plane in Munich the day before to give the plane more balast to cope with the storm winds", which is not a procedure I am familiar with. Increasing the aircraft weight will increase its inertia and therefore make it less susceptible to wind gusts. Let us assume they completely filled all fuel tanks in Munich.
The A320 has a fuel capacity of up to 27,200 l. Multiplying that with the density of Jet A-1 (0.804 kg/l at 15°C), gives about 21.87 t. This would make the total weight before payload at Vienna 63.36 t, therefore leaving 14.64 t for payload. Now this is lower than the maximum of 19.9 t. Using standard passenger weights in Winter of 195 lbs = 88.5 kg, this would allow 165 passengers. The A320 exit limit is 195 passengers. It is therefore possible that some passengers had to leave the plane to get below MTOW.

Awesome, thanks. I guess I could have low balled the number of people off, I was upfront so it was hard to judge and no one called the numbers out up front when we were discussing it. The filling of the plane with fuel thing might have been a red herring, one of the stewards said it, although they hinted it was to keep it more firmly planted on the ground during the storm, not to affect flight performance in any way.

@PhilShackleton Ah, that's interesting. Airliners don't have tie downs and are usually parked outside, but I've never heard of an airliner blown away in a storm :p

One point though, for the scenario of passengers disembarking to occur, the OEW would have exceeded the max landing weight wouldn't it? This is presuming they didn't refuel in Vienna.

@Bianfable, usually what happens is the airplane weathervanes around into the wind, rather than getting blown away outright.  There are a few videos of this sort of thing floating around on YouTube.

@PhilShackleton MLW (Maximum Landing Weight) of the A320 is 66t, so that scenario would not have left much room for passengers, only 2.64 t or 29 standard passengers.

@Bianfable It can happen. Some aircraft are more vulnerable to it than others of course. https://www.youtube.com/watch?v=nWriy_XGXfc shows a tornado playing with 737s, the winds from the storm that blew over Europe last weekend were similar in strength... https://www.youtube.com/watch?v=nrl3ex7w6nA and another 737 sliding around on icy tarmac in strong winds while parked. Notice the luggage handler trying to push it back :)

Yes it is. While waiting for a delayed departure from Dusseldorf some years ago, the ambient air temperature rose enough during the delay to reduce the density of the air enough that the plane was overweight for takeoff. They fixed the problem by pumping fuel out of the plane to bring it back within max limits.
We then hit headwinds on the flight to LAX and were forced to make an unscheduled stop in Winnipeg to refuel the plane because had the flight continued, it would have been burning its minimum reserves prior to arrival.
No one on that flight was very happy.

It always bugs me when people are dissatisfied when their safety is being put first...

It didn't bug me, I'm just inquisitive. I offered to disembark and arrived in Munich via train before the flight which the volunteers were offered landed. Considering the circumstances I was a happy customer. It's more seeking more knowledge than questioning their course of action, they clearly did the right thing, I just want to know more. I'd have asked the pilot, but he was a bit busy.

That doesn't sound so much like that aircraft was over fueled but simply exceeding another metric called maximum zero fuel weight or possibly the maximum ramp weight.  Refueling is not required to exceed this, if the aircraft is overbooked or has a particularly heavy load of passengers and/or cargo.  I suspect this was the motivation on the part of the flight crew to make the decision they did.


text:
Can a VFR flight reference a waypoint in communication?
Can a VFR flight reference an IFR Waypoint when communicating position to tower or centers?
For example: “N1234 at 3500’ at FERMY, request blah blah blah?”
Thanks
RHD!
****Adding additional circumstance after the last two responses. Apologies for not being able to comment inline but apparently given the length of the below text I must edit my original post. Sorry for any confusion. ***
After some thought on the answers I want to add a little more to the discussion and my situation that prompted the question. I am using more of an EFB solution as you can see from the screen shot. This is a heavily trafficked area of SoCal as well as multiple airspace’s under multiple controls butted up to one another. I use a display on FF which very clearly defines those airspace’s without a lot of study. Aeronautical map to be exact and then Jeppesen when necessary. This map is super clean and minimizes head down time when head up is critical. I was in a particular area where I was not 100% sure on the closets VFR reference point. What however was very clear was one of the primary IFR waypoints (just using FERMY in this example only). The amount of time for me to be able to reference my altitude and FERMY was less than two seconds. On the other hand, switching to VFR sectional refinding myself, finding nearest VFR point and communicating, was infinitely longer. Hence the prompting of the question. I see the importance of other VFR pilots also knowing my position is of course most critical in an uncontrolled or fringes of controlled airspace at same time I further expect Tower or Center to also reference my nearest landmark. So now a bit more info and two “needs” (tower knowledge of my location and of course fellow traffic) does this change the discussion at all?

Your edit does not really change the discussion based on your scenario. If you are in a radar controlled area, ATC can see the VFR traffic even if they are not talking to them. They can still provide separation. If you are talking on the VFR frequency of the local area, treat it like uncontrolled CTAF communications.

P. S. Always Sea and Avoid.

Nice guys.
Thanks again!

See and Avoid (darn spellcheck).

I figured it was some pilot humor I had not yet learned :-)

J. Hougaard is correct. With Tower, Approach and Center, yes you can use waypoints in communications. Be prepared for them not to know immediately where a lesser used waypoint is. I have had Center not know where particular Class G airports in their jurisdiction were. Some know the names by heart, but not the airport codes.
When it comes to communicating with FSS, best practice is to reference your position by distance and direction from a VOR. Especially on your initial call. If you are on a flight plan, reference the points in your flight plan. Referencing an airport will also work.
When communicating over CTAF, it is best not to use waypoints. Instead, use distance and direction from the airport. Even if you are flying IFR or you are on an IAP. Otherwise reference your position by very well known Visual Reference Points. Preferably ones that are charted on your sectional. There are a lot of non-instrument rated pilots who may also be flying. A waypoint may not mean anything to them. Lack of ATC will mean lack of separation control unless you communicate in a way that is universally understood using the lowest common denominators.

Good point about not using arbitrary waypoints when communicating on a CTAF or similar frequency

Really appreciate it!
Thank you
RHD

Yes you may, even if it is not so common. It can certainly make it easier for ATC to locate you quickly, especially if you are not so familiar with the local geography and VFR landmarks. Just remember that some IFR waypoints are used very rarely, so the controller might not immediately be sure of its position. So if you are near a common VFR reporting point, it is probably better to use that.


text:
How free are VTOL pilots to hover?
When piloting a Harrier or F35 can the pilot just hover at will?
Or is this possibly something that will eat up lots of fuel, and should only be done when planned? (like for landing)
Is spontaneously hovering even a thing? There are some media-depictions of these planes doing it (F35 hovering in Die Hard 4, Harrier hovering in True Lies, Harrier in Metal Gear Solid 2, etc)
I remember an article saying something like "VTOL takeoff is avoided, as then the plane needs to be air-refuelled immediately", but I haven't been able to find a good source for this.

Just FWIW, "at will" and "spontaneously" are kinda odd choices of wording here...  Like asking if a pilot can spontaneously, or at will, slow down and lower the flaps for landing.  It isn't totally clear what your confusion might be, but you have a good answer already so maybe I'm just being picky.

There are weight limitations associated with hovering and vertical landings. The F-35B, as I understand it, requires a A/C gross weight under 40,000 lbs in order to safely do this.  This roughly translates to no stores aboard the airplane, as well as an internal fuel load of only 40% or so of total capacity.  Harrier variants will have similar restrictions as well in regards to when a vertical takeoff or landing may be performed.
As the airplane will be operating close to full thrust during hover and/or vertical landing, it is consuming fuel at a great rate, so hovering operations are limited, generally only do a couple of minutes during final approach and landing during shipboard operations.  At terrestrial airports, the F-35B and Harrier generally perform conventional landings.  I also know, at least in the case of the F-35B, there are concerns about using the vertical lift system at terrestrial airports due to the risk of hot exhaust gas either cracking or damaging runways or parking aprons.
Due to the complexity of the lift fan system, an F-35B does not use it for anything aside from STOVL operations.  There may be speed limitations as well with engaging the lift fan system on that aircraft, possibly somewhere in the area of below 250 KIAS.  Harriers, however, could use nozzle position during all aspects of flight, including combat.  Marine Corps tests performed in the 1970s in both computer simulations and on actual aircraft revealed the potential for using VIFF (Vectored thrust In Forward Flight) for both offensive and defensive maneuvering of the jet.

VTOL pilots (and helicopter pilots) also prefer to avoid hovering unless necessary for another reason: safety.
Since the aircraft is operating at or close to 100% power output, if something in the propulsion system is going to break, it is more likely to break when under the greatest stress.
And when hovering, the pilot has the least number of options to deal with a  loss of power problem, as they are entirely dependent upon the engine(s) for control.
Generally speaking, helicopters and VTOL aircraft get into forward flight as soon as possible, and stay there as much as possible, as it reduces fuel consumption, reduces stress on the aircraft, and gives the pilot more time and options to deal with a potentially fatal problem.


text:
What's the reason for the local flap extensions at the shockbody locations?
This weekend I was on a Airbus A319, and I noticed that the flaps have small extensions at the location of the shockbodies (indicated in the picture with the red circles)
I was wondering what the reason is for these extensions?
My guess is that it could be to compensate for the lower local lift generation caused by the presence of the shock bodies, but I'm not sure. I'm also interested in knowing why they have different sizes at different locations.

My guess is that the top of the fairing has to be open allow room for the actuator hardware to move, so the flaps have those extensions to cover the section that is open.

.. and the lengths are the same when taken from the hinge.

@fooot pictures of flaps retracted support your guess. When retracted, thoses flaps extensions cover the shockbodies (almost) perfectly.

The anti-shock bodies also serve as fairings for the flap actuators. When the flaps are extended, the anti-shock bodies move down as the flap mechanisms extend. The upper surfaces of the anti-shock bodies are open to allow room for these mechanisms to extend.
The extensions to the flaps are to cover the openings of the anti-shock bodies when the flaps are retracted to provide a more aerodynamic surface. Evidently the outer locations have larger openings to cover.
Below is an image of a different aircraft and flap track design, but the principle is the same. You can see some of the hardware that sits in the fairings, and the covers that allow the hardware to extend out of the fairings.

Source
When the flaps are retracted, you can see that the flaps close out the top of the anti-shock bodies, and the outer position is closed out further aft.

Source

Great answer, perhaps you could add the picture from Manu H's comment to the question as well? I think it helps to illustrate your point.

I'm not sure, but I think that those are trim tabs.

Trim tabs on flaps? They seem to be pretty solidly connected to the rest of the flaps.

Trim tabs are usually located on ailerons, rudders and elevators and rarely extend further the flight control surface, as highlight by those pictures

Trim is used on control surfaces in order to keep the pilot from having to put constant pressure on the stick. Flaps don't have trim.

Aren't those flaperons, though? Airliners have mid-span ailerons that I think are also flaps.


text:
What is this wire going from mid-fuselage to the tail on this 737?
In  this question the following image is shown, with the question what the two bulges at the aft fuselage are.
However, I'm wondering what this wire is that starts somewhere midway the fuselage, and goes to the vertical stabilizer.
Is it also radar related?

Image Source

It is the HF antenna. It was mostly used in older aircraft, which used them in trans-oceanic flights or in areas without UHF or VHF communications facilities.Modern 737s (and other aircraft in general) have done away with them. On later versions it was fitted in the leading edge of the Vertical fin of B737-200s, as shown in the figure below.

Image from b737.org.uk
Note that these aircraft were delivered in 1982-83. Newer 737s don't have these.

So the wire was a part of the HF antenna? And the newer version don't need this wire anymore?

@ROIMaison Yes. The new antenna looks something like this

@aeroalias: That page seems to require an account to see it. Do you have any references that don't require an account?

@user2357112 Thats wierd. There seems to be no problem for me. Anyway, see this.

When you say "newer 737s don't have these," you're referring just to the long external wire antennas, not HF antennas in general, right? AFAIK, nearly all airliners still have HF antennas for the purposes you mentioned (i.e. trans-oceanic routes and such.)

You can tell it is an older-model 737 by the engine nacelle shape as well. (photo posted by OP)

@reirab Yes. I meant the external wire antennae. They've been shifted to the vertical fin, it seems.

What is the purpose of HF antenna on the  airplane except for HF communication?

@Arian - HF radios have to be used for trans-oceanic flights because VHF and UHF radios can not provide the increased range accomplished by bouncing the radio signal off of the ionosphere.

It is an HF (High Frequency) antenna. It is used for aircraft to communicate on overseas flights. VHF (Very High Frequency) airband radios are used for normal local and cross country flights.
For a radio to transmit effectively, the internal components of the radio and the external (to the radio) antennae both have to match the frequency used for the transmission. If either does not match, the signal will not go out as strong nor as far. The way the antennae match is by having an antenna that corresponds to the wavelength of the signal. The way you determine the length based on the signal frequency is by dividing 234 by the frequency in megahertz. This gives you your antennae length in feet. Therefore, the higher the frequency, the shorter the antenna needed.
For this next section, we will relate the radio wavelength to energy. The higher the frequency, the shorter the wavelength. In our examples, the shorter the wavelength, the more “energy” the radio wave (or signal) has.
The reason this is important is that radio signals travel in straight lines. They are just like light. They require a lot of energy to punch through obstacles. If the radio receiver is in the radio “shadow” of an obstacle, it will not receive the signal. Since the Earth is curved, this limits the distance a particular radio wave can be received from its source. The line-of-sight (straight line seeing) distance of an observer standing on the Earth’s surface in flat terrain is only 60 miles.
One way to combat this is to use lower frequencies. Frequencies of less than 30 MHz do not have enough of the required energy to punch through the protective obstacle surrounding the Earth called the ionosphere. Instead, the signal gets reflected back down towards the Earth where it gets reflected back up again. The signal will then bounce between sky and Earth for as long as it has energy to travel. Sort of like a billiard ball.
When traveling extremely long distances, like overseas, you have to utilize this signal bouncing feature of HF radios to reach your intended recipient. Radios in the UHF and VHF range can only be used as line-of-sight transmitters because, at frequencies above 30 MHz, the wavelength of their signals will punch through the ionosphere and not get reflected back down to Earth.
P.S. HF antennae can be bent or folded to accommodate less space. The antenna length can even be divided in half or fourth, but may induce frequency matching errors. Dividing it by eighth will compound those errors too much to make it useable in many cases. Any other division will make the antennae not match. To compensate for smaller antennae, internal components of the radio and electrical ballasts and counter-poises on the antennae are used to compensate for the shorter length.


text:
Is the "Red two standing by" dialog in Star Wars: A New Hope sensible for real fighter pilots?
This SFF.SE question: " Why did Red Squadron give their call signs in random order? " raises a good point: for some reason, the "Standing by" responses Red Squadron pilots give before attacking the Death Star in Star Wars Episode IV: A New Hope are out of order:

Red Leader: All wings report in.
  Red Ten: Red Ten standing by.
  Red Seven: Red Seven standing by.
  Biggs Darklighter: Red Three standing by.
  Porkins: Red Six standing by.
  Red Nine: Red Nine standing by.
  Wedge Antilles: Red Two standing by.
  Red Eleven: Red Eleven standing by.
  Luke Skywalker: Red Five standing by.
  Red Leader: Lock S-foils in attack position.

(to top off the mis-ordering, Red Eight and Red Four never respond).
This was of course answered in-Star-Wars-Universe, but I'd like a perspective of real aviation experts on this:

Is this protocol (all fighters in a group should report in by their call signs) based on something real fighter pilots would do (either WWII era pilots - since Star Wars fighter combat was famously based by Lucas on WWII - or 1970s era).
What is the main purpose of such a protocol? Communications check? Verifying who's flying? Verifying if someone has an issue? Team morale?
In light of #2, does the real life protocol have a specific order of responses, or is it as "whoever responds whenever" as in the Star Wars example?

DVK you should crowdsource this to puzzling stack exchange in the form of a riddle. If there is a pattern to be had, they will find it.

@corsiKa - I am extremely hesitant to participate in that particular SE, but you're welcome to post your idea if you want to, no objections from me.

Obligatory silly dialog reference:  "[the Millennium Falcon] once did the Kessel Run in 12 parsecs."

Tactical call signs are typically given in the format "word" "number" - "number".  For example, Camel 1-1.  In this example Camel 1-1 is the lead Camel in the Camel flight.  As you may have guessed, instructions are always acknowledged in order.  This helps the lead aircraft determine who may not have received the instruction (and some instructions are extremely time critical), or worse, in the event of an accident, determine (by lack of communication) who might be involved.  If someone does miss a comm, then typically the flight waits a few seconds and the next guy in line makes his radio call with the lead noting the person that was skipped.
Tactical call signs change with each flight, and may or may not have any real significance to the event being flown.  Funny ones are usually best; i.e., Camel works really well if you want to Alpha check a point called "Toe".
Here's a typical scenario: While practicing a 2v1 in the MOA (military operating area), Camel 1-2 gets a HYD caution, and has to stop the fight.
Camel 1-2 initiates with, "Camels knock it off, knock it off."
Next the flight reports back in order:

"Camel 1-1, knock it off."
"Camel 1-2, knock it off." (Even though Camel 1-2 initiated it, he still reports in order)
"Camel 1-3, knock it off."

I would say that Lucas came pretty close to replicating the actual sequence.  Sure, they're out of order and they're missing the "# - #" format, but its a decent attempt for Hollywood.

Does Camel 1-2 not identify that they're the one initiating the order?

@cpast Since at least in civilian formation work anyone can make the "knock-it-off" call (& everyone is expected to abide by it) I would imagine if you're calling a "Knock it off" identifying yourself in that call is less of a priority than making sure everyone in the flight knows to stop whatever they're doing and move to whatever safe positions/altitudes you defined before the mission. You can figure out who made the call when everyone is safe and stable.

Since I'm the one saying there might be some other reason they'd ask in a different order, I'll ask here - Is there any other order they might make these call signs in other than numeric order?  Or any reason some numbers might be skipped?

What's the point of having both a name and a first number? It seems like either a name or a first number would be enough to distinguish the different formations flying within radio range of each other

@cpast Voretaq is absolutely correct.  Knock it off's are treated as a quasi emergent situation and anyone can call them.  Since the greatest risk of a midair is generally the moments following a knock it off, everyone needs to expeditiously check in without trying to remember who already called what so that further deconfliction instructions can be issued.

@raptortech97 Because there might be several Camel divisions under the Camel call sign.  In this case Camel 1-1 is leading 1-2, 1-3 and 1-4, while Camel 2-1 is leading 2-2, 2-3 and 2-4.

One should also note that Lucas was inspired by the Dambusters, hence real air force experience, albeit from across the pond.

I'm a bit confused between the "urgent situation" scenario and "wait several seconds" if someone doesn't respond. In a larger flight those 2 ideas seem contradictory to each other.  Perhaps that should be a separate A.SE question...

"HYD" = "hydraulic"...?

Is there a particular reason to believe that the Word-Number-Number format is so ubiquitous that it's out-of-place for Star Wars to use it?  I'm not totally familiar with the WW2 flying Star Wars took to space, but word-number-number seems like modern usage.


text:
Can non-FAA towers employ foreigners?
I understand you must be a US citizen in order to work ATC with FAA.
Is it different with the non-FAA towers? Could I as a European citizen be employed (working visa/greencard) there?

14 CFR 65.31 and 65.33 do not mention citizenship as a requirement.
This job listing with Serco for a position at TTD says that you must:

Be eligible to work for Serco under the Federal Immigration Laws
Be able to receive an interim security suitability clearance granted by FAA Security derived from a public trust background check.

According to ClearanceJobs.com, US citizenship is not a requirement to be eligible for a Public Trust position.
So it seems like it would be possible for you to work at a contract tower. But this is the sort of question that you really should ask of the hiring manager at a specific company where you would like to work.


text:
What is the maximum amount of flight hours an aircraft can have a month?
The reason I ask this question is because I am a programmer and developing ETL processes to calculate reliability of products that are installed in aircrafts.
I have been getting A lot of bad data from the OEMs.
I have been told by an engineer at my organization that the maximum number of flight hours an aircraft can have is 400 hrs a month.
Is this accurate per FAA regulations?

As a programmer I would tell you to build your model on the assumption that the maximum number of flight hours an aircraft can accumulate in a month is 745: Flying 24 hours a day for 31 days (the most you can have in a month), plus one hour - "What if the plane is Air Force One & refuels mid-air for a month without landing?" This particular edge case is highly unlikely - it may even be impossible (I don't know how long a VC-25 can fly without any maintenance) - but why not handle it?

So you're a data analyst, not an embedded systems engineer, so I guess it's not as big of an issue, but Stack Exchange probably isn't the right place to get your system's requirements, is it? If you were an embedded systems engineer, it would be downright irresponsible.
Anyway, there's nothing in the FARs that limits flight time "by month". There are however air worthiness regs  (maintenance basically) that must be complied with.  These are going to vary based on the category of plane.
https://www.faa.gov/aircraft/air_cert/airworthiness_certification/std_awcert/std_awcert_regs/regs/

@Calphool I am not a data analyst.  The ETL process is only one component of implementation.  I am a solutions developer and developing a reliability management system.  Why so gung ho on the judgment?  Nor am I getting requirements here.  I was skeptical about flight hour data and thought one's with aviation experience might provide some insight.

@Calphool - I don't see a problem with seeking guidance here, especially for a non-critical component of his software. If it were true that there was a hard limit of 400 hours imposed by the FAA, he could code a warning in the ETL that the numbers appear to be out of range. If software engineers never used StackExchange for guidance, my company's developers would be a lot less productive :)

I don't think there is any regulation on max flying hours, just regulations on maintenance intervals.
The "A" check is the most frequent check, and according to Wikipedia:

This is performed approximately every 125 flight hours or 200–400
  cycles. It needs about 20–50 man-hours and is usually performed
  overnight at an airport gate or hangar. The actual occurrence of this
  check varies by aircraft type, the cycle count (takeoff and landing is
  considered an aircraft "cycle"), or the number of hours flown since
  the last check. The occurrence can be delayed by the airline if
  certain predetermined conditions are met.

The other checks include:

B check - every 4–6 months, requiring about 150 man-hours and is usually performed within 1–3 days at an airport hangar
C check -  every 20–24 months, requiring about 6000 man-hours, taking 1 to 2 weeks to complete
D check - major maintenance check, occuring about every 6 years, requiring 50,000 man hours, generally spanning a couple months.

Note that all of these times are approximate, depending on the exact maintenance plan filed by the airline and the aircraft type. Also cycle count may be factored into the maintenance intervals in addition to flight hours so aircraft that do many short-haul flights may have more frequent maintenance.
So in any case, only looking at the A checks, if you can land, refuel, service, and get back in the air in 2 hours between 10 hour flights, the plane could stay in the air for 20 hours/day. Every 6 days, it will need some downtime for the A checks, let's say the airline puts enough  people on it to get the check done in 5 hours. So that's 125 hours per cycle: 120 hours flying, 5 hours in maintenance. They can fit 4.83 of these cycles in a 30 day month so the aircraft could be flying up to 580 hours in any given month (but that last A check gets deferred to the next month, so that means less time in the air that month.
With longer flights (which reduces the overhead from turnaround times) and tighter turnaround times, the flight hours per month could be higher. If you really want the maximum for a month, then if you assume 125 hours per maintenance inverval and that the plane is kept in the air as long as possible with 0 turnaround time, that's around 690 flying hours out of 720 total hours in a month.
Of course, this makes a big assumption that the A check interval really is 120 hours, and that the time to do the maintenance is 5 hours, in the real world both numbers will vary based on aircraft, airline, and maintenance staffing levels.
Plus, over the longer term, you need to factor the other, less frequent but also more time consuming maintenance checks (B through D checks), as well as allow downtime for unexpected repairs.

Thank you for response...I am aware of the maintenance intervals...580 seems right...I wanted to take these intervals into consideration...you provided an awesome answer...+1 and answer accepted.

@user216392 Is there B Checks as well?

Yes, checks range from A - D with A being the most frequent (but fastest to complete, it's generally completed overnight) and D being the least frequent (every 6 years or so) but consuming the most time with around 50,000 man hours and 2 months real time being required for the check.